My invention concerns apparatus for the transfer (reading and writing) of data with magnetic disk media such as, typically, flexible magnetic disks commonly referred to as floppy disks. More specifically, my invention pertains to a read/write circuit of such data transfer apparatus or floppy disk drives featuring provisions for the reduction of voltage and power losses to a minimum.
In the art of digital data transfer with flexible magnetic disks, the magnetic read/write head has been known which has a center-tapped read/write coil, as disclosed for example in Morita et. al. U.S. Pat. No. 4,651,235. The two halves of the read/write coil, as so electrically divided by the center tap, are alternately excited during writing in accordance with the binary-coded write data signal. During reading, then, the center tap is not used, but the desired read data signal is derived from the output from the complete read/write coil.
A problem has existed with this known type of read/write head by reason of the inherent inductance of the read/write coil. as is well known, the inductive coil stores energy as a result of the flow of the write current therethrough. Consequently, the current magnitude in either half of the read/write coil does not immediately become zero each time the flow of the write current terminates. Were it not for a special circuit for taking up such residual current, resonance would take place in the coil due to an inductance-capacitance circuit composed of the inductance of the read/write coil, the capacitance between the conductors connected to each half of the coil and the ground, the capacitance between the conductors connected to both halves of the coil, etc. Thus an oscillatory current would flow through both halves of the coil for some time upon cessation of the flow of the write current through either half of the coil.
A known solution for the elimination of the oscillatory current is the provision of a circuit for the release of the energy stored in the read/write coil. The energy release circuit must be electrically isolated from the read circuit. Conventionally, therefore, a pair of diodes have been connected respectively between the two halves of the read/write coil and the pair of transistors for the alternate excitation of the coil halves, and a socalled write terminate resistor has been connected between the pair of write current lines each extending between one diode and one transistor. The write terminate resistor serves to release the undesired energy of the read/write coil therethrough and hence to reduce the oscillatory current. This known circuit arrangement is incorporated, for example, in the floppy disk drive read/write amplifier IC chip HA16642 manufactured by Hitachi Co., Ltd., as illustrated block-diagrammatically on page 67 of "The Latest Floppy Disk Drives and their Application Knowhow" published June 1984 by CQ Publishing Co., Ltd., of Tokyo, Japan.
I object to the prior art energy release circuit because of the connection of the diodes on the write current paths to the two halves of the read/write coil for isolating the write terminate resistor from the read circuit. I have ascertained by experiment that the diodes cause a voltage drop of approximately 0.7 volt, as well as power loss and heat production, thus running counter to the current demands for the less power consumption and lower voltage driving of magnetic disk apparatus.